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| United States Patent |
5,640,471
|
|
Khan
, et al.
|
June 17, 1997
|
Adiabatic tapered S-bends for compact digital switch arrays
Abstract
An optical switch array in an M.times.N configuration has a set of M input
digital optical Y-branches; a set of N output digital optical Y-branch;
and at least one S-bend interconnect waveguide connecting at least one
input digital optical Y-branch to at least one output digital optical
Y-branch, with the S-bend interconnect waveguide being adiabatically
tapered for providing adiabatic modal evolution between the at least one
input and output digital optical Y-branches. Each of the set of N output
digital optical Y-branches has an associated branch separation point; and
an output port of the at least one tapered S-bend interconnect waveguide
is connected substantially adjacent to a respective branch separation
point of a respective one of the set of N output digital optical Y-branch.
Compact digital optical switch arrays can be fabricated using such
adiabatically tapered S-bend interconnects to eliminate the overlap
sections of intermediate digital optical switch elements of the digital
optical switch array, and thus to reduce the overall length of the digital
optical switch array for providing improved propagation characteristics.
| Inventors:
|
Khan; Mujibun Nisa (Freehold, NJ);
Zucker; Jane Elisa (Aberdeen, NJ)
|
| Assignee:
|
Lucent Technologies Inc. (Murray Hill, NJ)
|
| Appl. No.:
|
581024 |
| Filed:
|
December 28, 1995 |
| Current U.S. Class: |
385/17; 385/16; 385/45 |
| Intern'l Class: |
G02B 006/28 |
| Field of Search: |
385/16,17,22,24,31,45
|
References Cited
U.S. Patent Documents
| 4232385 | Nov., 1980 | Hara et al. | 385/45.
|
| 5091981 | Feb., 1992 | Cunningham | 385/3.
|
| 5163106 | Nov., 1992 | Okayama et al. | 385/45.
|
| 5418868 | May., 1995 | Cohen et al. | 385/16.
|
Primary Examiner: Palmer; Phan T. H.
Claims
What is claimed is:
1. An optical switch array in an M.times.N configuration comprising:
a set of M input digital optical Y-branches;
a set of N output digital optical Y-branches; and
at least one S-bend interconnect waveguide connecting at least one input
digital optical Y-branch to at least one output digital optical Y-branch,
wherein the S-bend interconnect waveguide is adiabatically tapered to
provide adiabatic modal evolution between the at least one input and
output digital optical Y-branch.
2. The optical switch array of claim 1 wherein M and N are not
simultaneously equal to 2.
3. The optical switch array of claim 2 wherein N>2 when M .epsilon.{1,2}.
4. The optical switch array of claim 2 wherein M>2 when N .epsilon.{1,2}.
5. The optical switch array of claim 1 wherein each of the set of M output
digital optical Y-branches has an associated branch separation point; and
an output port of the at least one tapered S-bend interconnect waveguide is
connected substantially adjacent to a respective branch separation point
of a respective one of the set of M output digital optical Y-branches.
6. The optical switch array of claim 1 wherein M.noteq.2.
7. The optical switch array of claim 1 wherein N.noteq.2.
8. An optical switch array comprising:
an input Y-branch waveguide including:
an input region operatively connected to an input port for receiving
optical signals; and
a plurality of branch waveguides connected to the input region for
processing the optical signals to a respective output port;
an S-bend interconnect waveguide having an input port connected to an
output port of the input Y-branch waveguide; and
an output Y-branch waveguide including:
an input region; and
a plurality of branch waveguides connected to the input region of the
output Y-branch waveguide, each branch waveguide connected to an output
port;
wherein the S-bend interconnect waveguide is adiabatically tapered to
provide adiabatic modal evolution with respect to the input Y-branch
waveguide and the output Y-branch waveguide for single-mode signal
propagation.
9. The optical switch array of claim 8 wherein the input port of the output
Y-branch waveguide has an associated branch separation point; and
the output port of the tapered S-bend interconnect waveguide is connected
substantially adjacent to the branch separation point to provide for a
reduced overall length associated with the optical switch array.
10. An optical switch array in an M.times.N configuration comprising:
a set of M input digital optical Y-branches;
a set of N output digital optical Y-branches; and
at least one S-bend interconnect waveguide connecting at least one input
digital optical Y-branch to at least one output digital optical Y-branch,
wherein the S-bend interconnect waveguide is adiabatically tapered to
provide single-mode propagation of signals therethrough from at least one
of the set of M input digital optical Y-branches to at least one of the
set of N output digital optical Y-branches.
11. The optical switch array of claim 10 wherein the at least one S-bend
interconnect waveguide is adiabatically tapered to provide the single-mode
propagation of signals therethrough.
12. The optical switch array of claim 10 wherein each of the set of M
output digital optical Y-branches has an associated branch separation
point; and
an output port of the at least one tapered S-bend interconnect waveguide is
connected substantially adjacent to a respective branch separation point
of a respective one of the set of M output digital optical Y-branches.
13. The optical switch array of claim 10 wherein each input digital optical
Y-branch includes:
an input region operatively connected to an input port for receiving
optical signals; and
a plurality of branch waveguides connected to the input region for
processing the optical signals to a respective output port;
each S-bend interconnect waveguide includes an input port connected to an
output port of a respective input digital optical Y-branch, and each
S-bend interconnect waveguide is adiabatically tapered to provide
adiabatic modal evolution with respect to the input digital optical
Y-branch and the output digital optical Y-branch for single-mode signal
propagation; and
each output digital optical Y-branch includes:
an input region; and
a plurality of branch waveguides connected to the input region of the
respective output digital optical Y-branch, each branch waveguide
connected to an output port.
14. The optical switch array of claim 13 wherein the respective input ports
of the respective output digital optical Y-branches have an associated
branch separation point; and
each respective output port of the tapered S-bend interconnect waveguide is
connected substantially adjacent to the branch separation point to provide
for a reduced overall length associated with the optical switch array.
15. The optical switch array of claim 10 wherein M.noteq.2.
16. The optical switch array of claim 10 wherein N.noteq.2.
17. The optical switch array of claim 10 wherein M and N are not
simultaneously equal to 2.
18. The optical switch array of claim 10 wherein N>2 when M .epsilon.{1,2}.
19. The optical switch array of claim 10 wherein M>2 when N .epsilon.{1,2}.
20. The optical switch array of claim 10 wherein M=N=4, and the overall
longitudinal length of the optical switch array is about 7 mm.
Description
BACKGROUND INFORMATION
1. Technical Field
This disclosure relates to digital optical switch arrays, and in particular
to tapered waveguide S-bend interconnects for digital switch arrays.
2. Description of the Related Art
Digital optical switches (DOS) and switch arrays are increasingly replacing
other types of optical switching devices in a wide variety of
applications, including communication systems.
Conventional DOS with no shaping; i.e. having only a single small angle,
are typically very long. Such long length can contribute to unacceptable
propagation losses, and can also lead to reduced fabrication yields.
Switch arrays including such conventional DOS as Y-branch waveguide
switches can be connected with S-bend interconnects with acceptable radii
of curvature; i.e. waveguides shaped like an "S" having optical
propagation losses that are not substantially increased. However, by
employing such conventional DOS, such switch arrays are also very long,
and therefore are not attractive.
Typically, there is an appreciable amount of overlap of branches in a
conventional DOS, which contribute to the overall length of the DOS. For
example, about two-thirds of the length of a switch array using DOS can be
attributed to overlap of branches.
SUMMARY
It is recognized herein that compact DOS arrays can be fabricated using
adiabatically tapered S-bend interconnects to eliminate a substantial
portion of the overlap sections of intermediate DOS elements of the DOS
array, and thus to reduce the overall length of the DOS array for
providing improved propagation characteristics and for saving on material
costs.
An optical switch array in an M.times.N configuration is disclosed having a
set of M input digital optical Y-branches; a set of N output digital
optical Y-branches; and at least one S-bend interconnect waveguide
connecting at least one input digital optical Y-branch to at least one
output digital optical Y-branch, with the S-bend interconnect waveguide
width being adiabatically tapered for providing adiabatic modal evolution
between the at least one input and output digital optical Y-branches. Each
of the set of N output digital optical Y-branches has an associated branch
separation point; and an output port of the at least one tapered S-bend
interconnect waveguide is connected substantially adjacent to a respective
branch separation point of a respective one of the set of N output digital
optical Y-branches.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the disclosed DOS array will become more readily apparent
and can be better understood by referring to the following detailed
description of an illustrative embodiment, taken in conjunction with the
accompanying drawings, in which:
FIG. 1 illustrates a switching stage for use in a DOS array;
FIG. 2 illustrates an expanded view of a branch separation point in a DOS
array; and
FIG. 3 illustrates a 4.times.4 input/output implementation of the disclosed
DOS array using adiabatically tapered S-bend interconnects.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now in specific detail to the drawings, with like reference
numerals identifying similar or identical elements, as shown in FIGS. 1-3,
the present disclosure describes DOS arrays using adiabatic tapered S-bend
interconnects for providing a compact configuration of the DOS arrays.
As shown in FIG. 1, switching section 10 of the disclosed DOS array
provides for 1.times.2 switching and has input section 12 of first
Y-branch 14 of the 1.times.2 switch with a relatively short length of
about 2 mm and an initial width w.sub.i, narrow enough to support only
single-mode operation, for receiving input light signals 16 at an input
port. Input section 12 is adiabatically tapered to have a final width
w.sub.f at a distance of about 1 mm from the input port for receiving
input light signals 16. In switching section 10, w.sub.f >w.sub.i for
conveying such input light signals 16 in single-mode propagation to
overlapping branch waveguides 18, 20. Each of branch waveguides has a
width w.sub.i and is separated by an angle .theta. of about 0.1.degree.,
with the branch separation point being about 0.5 mm to about 2 mm from the
width w.sub.f. In one embodiment, w.sub.i is about 2 .mu.m and w.sub.f is
about 6 .mu.m.
First Y-branch 14 can be operated by applying a switching signal to change
the refractive index of one branch with respect to the other.
Input section 12 conveys such light signals 16 to branch waveguides 18 or
20 and then to adiabatically tapered S-bend interconnects 22 or 24 which
Join branch waveguides 18 and 20 at input regions 26 and 28, respectively.
Each S-bend interconnect 22, 24 is adiabatically tapered from a narrow
initial width w.sub.i at input regions 26, 28, respectively, to a wider
width w.sub.f at output regions 30, 32, respectively.
Such initial widths w.sub.i of first Y-branch 14 and each tapered S-bend
interconnect 22, 24 are identical, and the final wider widths w.sub.f of
first Y-branch 14 and S-bend interconnects 22, 24 are identical as well.
The adiabatic tapering of S-bend interconnects 22, 24 from width w.sub.i
to width w.sub.f thus maintains single-mode propagation of the optical
signals.
Output regions 30, 32 join Y-branches 34, 36 substantially close to the
branch separation points of the respective branch waveguides of Y-branches
34, 36, which eliminates the need for relatively long joint sections of
Y-branches 34, 36. Accordingly, the entire length of each intermediate
switching section of a DOS array is shorter than corresponding switching
sections of DOS array switching stages in the prior art.
Each of Y-branches 34, 36 has a width w.sub.f substantially near the branch
separation points, and overlapping branch waveguides have a width .sub.i,
so single-mode propagation of optical signals is maintained.
Portion 38 of Y-branches 14, 34, and 36 is shown in FIG. 2, with central
region 40 having a width w.sub.f for conveying optical signals in
single-mode propagation, and overlapping branch waveguides having widths
w.sub.i. The length of central region 40 between the width w.sub.f and the
branch separation point is about 0.5 mm in this example. Accordingly,
other waveguide elements for propagating signals in single-mode
propagation such as S-bend interconnects 22, 24 can be joined
substantially close to the branch separation point of the next Y-branch in
the array to maintain such single-mode propagation.
As shown in FIG. 3, M.times.N DOS arrays can be fabricated with a plurality
of switching stages having such switching sections 10 shown in FIG. 1.
Using the adiabatic tapered S-bend interconnects, the M.times.N DOS arrays
provide for a more compact design with multiple switching stages, with
M.noteq.2 and/or N.noteq.2. In the case where M=1, N must be greater than
2, and where N=1, M must be greater than 2. Also, if M=2, then N must be
greater than 2, and if N=2, then M must be greater than 2. In an exemplary
embodiment, DOS array 42 shown in FIG. 3 is a 4.times.4 non-blocking
array, thus capable of switching 4 inputs to 4 outputs in response to
switching signals applied to the respective Y-branch in each switching
stage. Each switching section can either switch from one input to two
outputs, or from two inputs to one output.
DOS array 42 includes input stage 44 and output stage 46, with at least one
intermediate switching stage therebetween. Each of stages 44, 46 includes
a plurality of single-mode waveguides 48, 50 with the same single-mode
width w.sub.i, respectively, which are part of the input DOS switches of
the array. Waveguides 48 of input stage 44 can be relatively long so that
the propagation of only the fundamental mode from the input is assured to
achieve adiabatic modal evolution to the switching branch with higher
refractive index values of the later stages.
The 1.times.2 stage 52, the 2.times.1 stage 60, and the intermediate
switching stages 54-58 employ switching sections and tapered S-bend
interconnects as shown in FIG. 1, respectively, and so are relatively
compact. For example, 1.times.2 stage 52 can include at least one Y-branch
62 connected to one of the input waveguides and having branch waveguides
64, 66 connected to input ports of adiabatically tapered S-bend
interconnects 68, 70, respectively, with each S-bend interconnect 68, 70
connected substantially close to respective branch separation points 72,
74, of Y-branches in another stage 56, respectively.
Conversely, 2.times.1 stage 60 can include adiabatically tapered S-bend
interconnects 76, 78 having input ports connected substantially close to
respective branch separation points 80, 82 of respective Y-branches 84, 86
in switching stage 58. Each of waveguides 76, 78 has output ports
connected to branch waveguides of Y-branch 88 which is then connected to
one of output waveguides 50.
By using such tapered S-bend interconnects connected substantially close to
the branch separation points of Y-branches in the intermediate switching
stages, the overall length of DOS array 42 is effectively reduced, with
the adiabatic tapering of the S-bend interconnects maintaining single-mode
propagation.
Typically, for a conventional 4.times.4 DOS array, the length is about 12
mm. DOS 42 using tapered S-bend interconnects connected substantially near
the branch separation points has a reduced overall length of about 7 mm,
which is a significant decrease over conventional DOS arrays. This
reduction in overall length is advantageous as the number of input and
output ports increases, since larger M.times.N arrays would employ many
more intermediate switching stages of switching elements, with each stage
contributing to the length of DOS array 42.
While the disclosed DOS array has been particularly shown and described
with reference to the preferred embodiments, it is understood by those
skilled in the art that various modifications in form and detail can be
made therein.
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